In a communication system for a vehicle, failure caused by various combinations attributed to a large amount of information may occur. For example, even if a user finds failure of one controller before the user takes a vehicle to an auto repair shop, the auto repair shop may not find the failure during failure diagnosis at the auto repair shop. To solve such an incident, a device disclosed in JP-A-2007-290540 is proposed. In the device, a communication history of data transmitted and received from the vehicle via a network is stored, and the failure diagnosis of a controller is performed with using the communication history. The diagnosis result is displayed on a display device, and stored in the device. In this case, the failure controller is easily specified based on the diagnosis result.
In a case where a communication system for a vehicle, which is capable of performing failure diagnosis, is used under a certain special condition, for example, in a case where the communication system is used under a condition that only a part of in-vehicle devices other than the controller is energized from a power source, the device may determine that the controller may be down even though the controller is normal. Specifically, when the failure diagnosis of the communication system is performed, the device may store the failure history of the controller such that the controller is not normal since the controller not energized from the power source cannot transmit and receive data via the network. The certain special condition realizes, for example, when the vehicle is shipped on a car carrier for export. In this case, in order to reduce discharge of a battery, only minimum in-vehicle devices are energized from the power source. The minimum in-vehicle devices such as a starter, an engine ECU and an air conditioner are necessary to operate the vehicle when an engine of the vehicle runs. Thus, in general, the communication device for the vehicle is not energized. In some cases, the communication device may be energized, for example, when the communication device performs an operation function of the air conditioner.
If a mechanic of a car dealer in an export country checks the vehicle, which has been used under a condition that the part of in-vehicle devices is energized from the power source, the mechanic finds the failure history of the vehicle. In this case, the mechanic considers that the controller corresponding to the failure history is down. Further, the mechanic may replace the controller with a new one. Since the controller is normal although the controller is not energized from the power source, the failure history should be deleted.